At present, in micromachining a substrate, forming an unevenness pattern (e.g., a resist pattern) on a substrate (e.g., a semiconductor wafer) using a photolithography technology is widely and generally performed. In order to finely process the substrate, various coating liquids are ejected toward a surface of the substrate from an ejection port of a nozzle
Japanese Patent Laid-Open Publication No. 2001-239199 discloses a coating liquid coating method, in which ejecting a coating liquid from an ejection port of a nozzle to a surface of a substrate in rotation while moving the nozzle along the surface of the substrate is disclosed as one exemplary embodiment for forming a coating film on a surface of a substrate. Thus, the coating liquid is coated on the surface of the substrate in a spiral shape. In this case, as compared with a so-called spin coat method that coats a coating liquid on the entire surface of a substrate using a centrifugal force by rotating the substrate after ejecting the coating liquid to the central portion of the substrate, the coating liquid can be saved, and the film thickness of the coating film can be controlled in a direction from the rotational center of the substrate to the peripheral edge of the substrate. However, since the surface of the substrate is not completely flat, the film thickness of the coating film may vary according to the height of the surface of the substrate even with the method disclosed in Japanese Patent Laid-Open Publication No. 2001-239199.
The coating liquid coating method disclosed in Japanese Patent Laid-Open Publication No. 2005-251864 includes: a plate thickness measurement process of measuring the plate thickness of the substrate in advance, an adjustment process of adjusting a separation distance (gap) between the ejection port of the nozzle and a stage on which the substrate is placed, based on the measured plate thickness of the substrate, and an ejection process of ejecting the coating liquid to the surface of the substrate from the ejection port of the ejection nozzle. With this method, since the gap between the surface of the substrate and the ejection port of the nozzle is maintained constantly, a coating film having a substantially uniform film thickness is formed on the surface of the substrate.
Japanese Patent Laid-Open Publication No. 2005-251864 discloses, as a plate thickness measurement method for measuring a plate thickness of a substrate in advance, (1) calculating the plate thickness of the substrate based on a region shielded by the plate thickness of the substrate, using a one-dimensional semiconductor laser array that projects parallel rays distributed in a vertical direction (in the thickness direction of the substrate, and (2) emitting light beams obliquely with respect to a predetermined location of the substrate from the rear side of the substrate and calculating the plate thickness of the substrate based on a light reception position of the reflected light thereof. Thus, in the adjustment process, the gap adjustment is performed by assuming that the plate thickness of the substrate is substantially constant within the substrate plane.